1. Field of the Invention
The present invention relates to a transmitter equipped with a cell switching function, and more particularly to a transmitter adapted for mapping and demapping of synchronous frames containing ATM cells of multiple channels.
2. Description of the Related Art
In the known public transmission network, audio signals and data information are transmitted to be processed via an infrastructure of SONET (Synchronous Optical Network) in a format of STM (Synchronous Transfer Mode). Such service signals according to the STM format are accessed, in each transmitter, at an STS-1 (Synchronous Transport Signal: 51.84 MHz) level conforming with the SONET frame format or a VT (Virtual Tributary: 1.726 MHz) level. External interfaces employed therefor conform with OC-48 (optical signal: 2.4 GHz), OC-12 (optical signal: 600 MHz), OC-3 (optical signal: 150 MHz), DS3 (electric signal: 44.736 MHz), DS1 (electric signal: 1.544 MHz) and so forth. Further, there is practically used of late a data information service which is based on the ATM (Asynchronous Transfer Mode) signal format to realize effective utilization of transmission lines and the band of transmission equipment.
Recently, eager demand is noticed in respect of a transmitter having, in particular, a cell switching function relative to ATM signals of multiple channels for achieving services with ATM signals while running the existing SONET network or the like. However, any transmitter equipped with such a switching function for STM signals and ATM cells has not been available heretofore. When STM signals of multiple channels to be switched are mapped to an STS-1 signal, the mapping positions of the individual channel signals multiplexed to the STM signals are predetermined, so that the signals of the individual channels may be mapped to the relevant frame positions of the STS-1 signal. Also in routing the STM signal of the each channel mapped to the STS-1 signal, it has been possible heretofore to achieve easy routing since the relevant channel can be detected from the corresponding frame position of the STS-1 signal.
However, when connecting a multi-channel ATM network to a SONET network or the like, there may be adopted a method of allocating one channel of each ATM cell to one channel of the STS-1 signal; or when mapping multi-channel ATM cells to one channel of the STS-1 signal, there may be adopted a method of mapping the ATM cells after determining the mapping position of each channel of the ATM cells in the same manner as the method relative to the STM signal. In the former case of allocating ATM cells to one channel, the number of required STS-1 channels becomes equal to that of the channels of ATM cells. Using many STS-1 channels signifies an increase of the number of physical paths in the transmitter, whereby a cross-connector and other devices employed for switching the ATM cells are rendered greater to consequently raise a problem that the transmitter as a whole is also enlarged in scale. Meanwhile, in the latter case of allocating ATM cells to multiple channels, some density nonuniformity is caused in the STS-1 signal due to the density nonuniformity of the multi-channel ATM cells, so that any low-density channel portion in the STS-1 signal is not usable for any high-density channel of the ATM cells to eventually result in an extreme inefficiency.
The ATM cells are routed in accordance with VPI/VCI which represent logical addresses stored in an ATM header, and then each ATM cell is transmitted to the relevant network. Since a logical connection is set per network (per ATM channel), there may occur a case where the same logical address is set in different ATM channels. In such a case, if each channel mapping position is not determined, it becomes impossible to identify the respective channels of the ATM cells mapped to the STS-1 signal, hence raising another problem that proper routing to the relevant network fails to be performed. In addition, there may arise a further problem that, since no discrimination is executable between the channels when the ATM cells mapped to the STS-1 signal are distributed to the relevant channels, exact distribution to the individual channels is rendered impossible.
It is therefore an object of the present invention to provide a transmitter capable of efficiently mapping ATM cells of multiple channels to one STS-1 signal.
Another object of the present invention resides in providing a transmitter which is capable of routing ATM cells to any interface module from an interface module containing multiple channels.
And a further object of the present invention is to provide a transmitter capable of routing ATM cells from any interface module to any network of an interface module containing multiple channels.
In accordance with an aspect of the present invention, there is provided a transmitter equipped with a cell switching function and having an interface module to serve as an interface between ATM cells and synchronous frames. The transmitter comprises a plurality of first physical paths for inputting ATM cells with channel identifiers given thereto to identify channels respectively; a second physical path for outputting the synchronous frame signal; channel identifier insertion means for inserting the channel identifiers, which are given to the first physical paths where the ATM cells are inputted, into predetermined areas of the ATM cells; and mapping means for mapping the multi-channel ATM cells, where the channel identifiers are inserted, to one synchronous frame signal and outputting the same to the second physical path.
Preferably, a detection means is incorporated in the interface module for detecting whether a predetermined value is set or not in the predetermined area of each ATM cell, and discarding any ATM cell where the predetermined value is not set.
In the above structure, when the interface module contains multiple channels, channel identifiers are previously given respectively to the individual first physical paths in the interface module. The channel identifier insertion means inserts the channel identifier given to the relevant first physical path into a predetermined area (e.g., cell header) of the ATM cell inputted from the first physical path. The mapping means maps the multi-channel ATM cells, where the channel identifiers are inserted, to the synchronous frame signal. Since the channel identifiers are inserted in the ATM cells mapped to the synchronous frame signal, any ATM cell can be identified with respect to the relevant channel, so that proper routing thereof to desired channels can be performed when the interface module is used in the transmitter.
In accordance with another aspect of the present invention, there is provided a transmitter equipped with a cell switching function and having an interface module to serve as an interface between ATM cells and synchronous frames. The transmitter comprises a plurality of first physical paths for inputting ATM cells with channel identifiers given thereto to identify channels respectively; a second physical path for inputting a synchronous frame signal where multi-channel ATM cells are mapped; and demapping means for demapping the ATM cells mapped to the synchronous frame signal and outputting the ATM cells to the first physical paths corresponding to the channel identifiers inserted into the predetermined areas of the ATM cells.
Preferably, a detection means is incorporated in the interface module for detecting whether the value in the predetermined area of each ATM cell is coincident or not with any of the channel identifiers, and the ATM cell is discarded if the result of such detection signifies no coincidence with any of the channel identifiers.
A channel identifier is previously given to each of first physical paths. The demapping means demaps the ATM cells mapped to the synchronous frame signal inputted from the second physical paths, and outputs each ATM cell to the relevant first physical path having the channel identifier inserted into the predetermined area of the ATM cell. Consequently, even in case the interface module contains multiple channels, it becomes possible to output the ATM cell to the relevant desired channel.
In accordance with a further aspect of the present invention, there is provided a transmitter having a cell switch module for routing ATM cells. The transmitter comprises a plurality of first physical paths for inputting a first synchronous frame signal where the ATM cells are mapped; a plurality of second physical paths for outputting a second synchronous frame signal; demapping means for demapping the ATM cells mapped to the first synchronous frame signal inputted from each of the first physical paths; mapping means incorporated correspondingly to the second physical paths for mapping the input ATM cells to the second synchronous frame signal; an identifier conversion table containing items which include routing information relative to the first physical paths where the first synchronous frame signal is inputted, logical addresses of the ATM cells, input-source channel identifiers in case the first synchronous frame signal holds multi-channel ATM cells, routing information relative to the output destinations of the ATM cells, and channel identifiers of the output destinations of the ATM cells in case the second synchronous frame signal, where the ATM cells are mapped, holds the multi-channel ATM cells; cross-connect means for outputting the ATM cells to the relevant mapping means on the basis of the routing information which conforms with the channel identifiers and the logical addresses of the ATM cells inputted from the first physical path; and a channel identifier update means for inserting the relevant channel identifier into the predetermined area of the first ATM cell on the basis of the routing information and the logical address relative to the first ATM cell in case the second synchronous frame signal, where the first ATM cells is mapped, holds the multi-channel ATM cells.
In the structure mentioned, the identifier conversion table contains items including the input-source channel identifiers in case the first synchronous frame signal holds multi-channel ATM cells, and the output-destination channel identifiers in case the second synchronous frame signal holds multiple-channel ATM cells. When the first synchronous frame signal holds multi-channel ATM cells, the cross-connect means acquires the routing information on the basis of the logical address and the channel identifier inserted into the predetermined area of each ATM cell, and then outputs the same to the relevant mapping means in response to such routing information. Consequently, even in case the ATM cells of different channels having coincident logical addresses are mapped to the same first synchronous frame, each ATM cell can be routed to the desired output destination properly. Further in case the multi-channel ATM cells are mapped to the second synchronous frame, the channel identifier update means acquires, from the identifier conversion table, the routing information and the output-destination channel identifier on the basis of the logical addresses of the ATM cells, and then inserts the output-destination channel identifier into the predetermined area of the relevant ATM cell. Consequently, when the interface module inputs the second synchronous frame where the multi-channel ATM cells are mapped, each ATM cell can be routed to the relevant channel corresponding to the channel identifier.
In accordance with a still further aspect of the present invention, there is provided a transmitter using the aforementioned interface module and cell switch module, wherein each ATM cell can be routed properly to a desired interface module from the interface module containing multiple channels, and also each ATM cell can be routed from any interface module to a desired channel of the interface module containing multiple channels.
The above and other objects, features and advantages of the present invention and the manner of realizing them will become more apparent, and the invention itself will best be understood from a study of the following description and appended claims with reference to the attached drawings showing some preferred embodiments of the invention.